Fluorescent discharge tube



Mrch l5, 1949.

c. P. BOUCHER ETAL FLUORESCENT DISCHARGE TUBE Original Filed July 14,1941 Patented Mar, l5,

FLUORESCENT DISCHARGE TUBE Charles Philippe Boucher, Atlanta, Ga., andFrederick August Kuhl, Ridgewood, N. J., assignors, by mesneassignments, to National Inventions Corporation, a corporation of NewJersey Original application July 14, 1941, Serial No. 402,412. Dividedand this application December 22, 1943, Serial No. 515,230

' 1 Claim.

This application for patent is a division of our copending applicationSerial No. 402,412, led July 14, 1941, entitled Luminescent tube systemand apparatus now Patent 2,351,914 of June 20, 1944, and the inventionrelates to uorescent tube lighting, and more particularly concerns amethod and manner of operating the present-day hot cathode fluorescentgas discharge tubes, which are now widely available on the market, oncoldcathode operation.

The advantages which are attendant upon the operation of fluorescent gasdischarge tubes on cold-cathode operation, with energy provided by highleakage reactance transformers which automatically provide the voltagesrequired for satisfactory operation, including both the required highstarting voltage and the lower operating Serial No. 402,411, filed July14, 1941, now Patent 2,317,844 of April27, 1943. Only casual mention ismade there, however, as to the feasibility of the satisfactory use insuch cold systems of tubes which are readily available on the market butwhich are initially designed for hot-cathode operation, and theconsequent achievement of material saving in initial investment. Nomanner of connecting nor mode of operating the hotcathode tubes isdescribed in either said application.

An important object of our invention, therefore, is to provide for thesatisfactory employment of hot-cathode uorescent gas discharge tubes oncold-cathode operation. Another object is to produce va socket for thereception of a hotcathode fluorescent. gas discharge tube in such mannerthat the tube will perform satisfactorily on cold-cathode operation.

Other objects and advantages in part will-be obvious and in part pointedout hereinafter.

In the drawing, Figure lis a perspective view showing a hot-cathodeuorescent tube adapted for cold-cathode operation in accordance with ourinvention, and Figure 2 is an exploded perspective view showing one formof socket which may be employed according to our invention, as Well asthe manner in which the same is associated with the terminals of a'.typical hotcathode uorescent gas discharge tube which can now be readilypurchased on the market.

As conducive to a more thorough understanding of our invention, we maysay at this time that the use of fluorescent gas discharge tube lightinghas sprung into considerable prominence during the last few years invarious industrial and commercial elds, as well as in householdlighting. Such fluorescent tube lighting in fact shows evidence ofsubstantially replacing the more conventional incandescent iilamentlighting in many elds of illumination.

The presence of the oxide-coated iilamentary cathode relied upon in theoperation of hotcathode tubes to provide the electron emission necessaryto prepare such tubes to support the arc discharge, and for aiding inthe maintenance of the arc once it is Struck, represents a source ofweakness. As the tube ages, the electronemitting properties of thecoating diminishes, and the coating tends to volatilize oif, or to chipoff under ionic bombardment. Both starting and maintenance of the arcdischarge at prevailing voltages becomes increasily diiiicult, and thearc becomes unstable in its characteristics. Blackening of the tube inthe region of the electrodes is found to occur, due to the depositingthereon of the coated material violatilized from the cathodes.

Although the preliminary heating of the lamentary cathodes prepares thearc discharge path for striking ,an 'arc thereacross at comparativelylow potential gradient between the electrodes, with consequentcomparatively high. power-factor and minimum sputtering of the cathodemetal, it is apparent that once the arc strikes, the arc tends tolfollow the path of the maximum ionization and to settle on the hottestpoint of the filament. Since sputtering inevitably follows thatphenomenon, the filament becomes thinner at this point, increasing inresistance. Because of the IRdrop in the region of the lament,therefore, this point of weakness becomes the hottest point along thecathode. Repeated settling .of the arc thereon eventually causes failureof the lament at that point. This of course ends the useful life of atube whereused on hot cathode operation. These lamentary cathodes areformed of small diameter tungsten wire, and consequently are somewhatfragile. Al-

though the tungsten metal possesses strong molecular cohesion at hightemperatures, the positive ionization bombardment which takes placeduring arc discharge is such that after about 2500 hours of operation,the filament wire is broken through and the lamp becomes normallyinoperative.

An important object of our invention therefore is to remove in largemeasure the difliculties and disadvantages set forth in the foregoing,and to produce a system for operating known fluorescent gas dischargetubes on cold-cathode operation, in which the tubes have stableoperating characteristics over a useful life span substantially inexcess of that hitherto possible of achievement.

One of the few disadvantages of the presentday fluorescent lighting ascompared to the conventional incandescent filament bulbs, is that whilethe filamentary bulbs emit useful light as soon as they are energized,it requires at a minimum, some 6 or 7 seconds in which to strike an arcacross hot cathode tubes 'in fluorescent lighting systems. Thisrepresents an appreciable time lag, and in many installations and usesis found to be a highly objectionable source of annoyance. Further,because such hot-cathode as are currently in use are designed to operateon low voltage input, it is impossible to reduce the impressed voltageto any material extent or to start or operate the tubes satisfactorilyon what may be termed dimmer operation.

A further object of our invention, therefore, is to produce a system ofoperating hot-cathode tubes oncold-cathode operation in such manner thatthey have extremely satisfactory starting characteristics and aresusceptible to satisfactory performance under dimmer operation, and inwhich system the occurrence of a broken filament in the fluorescent tubeinterposes no problem. A still further important object 'of ourinvention is to produce a fluorescent light systern employing insatisfactory cold-cathode operation, the known hot-cathode tubes readilyavailable on the market, and in which system, the size and physicalshape of the electrodes of the tube are unimportant.

Referring now more specifically to Figures 1 and 2, wherein is discloseda preferred embodiment of our invention.

The tube T1, T2 is of the hot-cathode type, having filamentaryelectrodes led out to pairs of exteriorly extending terminals, whichterminals are short-circuited for our desired cold-cathode operation.The tube is lined with suitable uorescent salts, to give rise to thedesired secondary visible radiation.

Accordingly, we have evolved an ingenious method of operating theseknown hot-cathode tubes on cold-cathode operation, which will now beelaborated upon, having reference to Figure 2. Here the tube consists ofa glass cylinder 3l interiorly lined with a suitable fluorescent salt.

`Filamentary electrodes, not shown, are disposed realized, however, isthe short-circuiting of these filaments.

To illustrate, the socket may be somewhat of the bayonet type, in whichthe lamp terminals and base are inserted into the socket and are lockedin place by a slight rotary twist. The socket in such case is designedto short-circuit the terminals of the lamp. The design may be such thatat the same time, a connection of the primary coil across the source ofenergy is established. This last feature is developed in our co-pendingapplication Serial No. 402,413, led July 14, 1941, now Patent 2,351,915of June 20, 1944, and will not be enlarged upon here. A special jumpermay be designed for dropping into the base of the ordinary socket, andis held in place, short-circuiting the tube terminals, by the base ofthe tube when the latter is positioned in thel socket.

For purposes of illustration, however, we disclose a socket indicatedgenerally at 34 and comprising a shell 35 of metal or suitable plastic.Within this shell and disposed in insulated relation thereto aremetallic conduits 36, 31 for receiving the prongs 32, 33, respectively,of the tube 3|. A metal jumper 38 is disposed Within the shell,electrically connecting together the conduits 36, 31, and therebyshort-circuiting them. A lead 39 to the associated secondary coilextends from the unit consisting of the two conduits and the jumper tothe exterior through a cap 40 on the shell 35. In this manner the unitconsisting of the prongs 32, 33 and the lamentary electrodes areelectrically connected together and form a single electrode. The base 4Iof the tube may consist either of metal or suitable plastic, just as thetube is found on the market. Since,

f however, this base is insulated from the prongs 32, 33, the questionof Whether it is formed of metalor of a plastic is a matter of but smallmoment, Short-circuiting the terminals adapts the tube for cold-cathodeoperation, and permits obtaining the manifold advantages referred tohereinbefore.

It will be readily appreciated that the invention described herein givesrise to many practical advantages not hitherto possible of achievementWith the equipment at hand. Our invention makes it possible to adapttubes already available on the market for service in our new electricalsystem, with increased tube life, much quicker starting characteristics,and with highly stable arc discharge, even with prevailing cold weather.

We find that, especially under steady operating conditions, the tubesemployed in accordance with our present teachings, give a much largersaving in power demand in the tubes, for the same light output. Forexample, We nd that under similar conditions, and with the samebrilliance in light output, our system requires only 380 milliamperes,whereas the known hot-cathode tube `systems require 420 milliamperes.

We claim:

In combination, a fluorescent gas discharge tube having at each endthereof a lamentary cathode and a pair of projecting prongs connectedthereto for insertion in a supporting and energizing socket, and a pairof metal jumpers one abutting and interconnecting one pair of saidprojecting prongs and the other abutting and interconnecting the otherpair, for short-circuiting the same and adapting the tube for initialand continued cold-cathode operation.

CHARLES PHILIPPE BOUCHER. FREDERICK AUGUST KUHL.

(References on following page) McKeag Dec. 3, 1940 Name Date SpannerJuly 15, 1941 Gaidies July 29, 1941 Inman Oct. 14, 1941 Schaefer Dec. 2,1941 yRussell v Sept. 15, 1942 Scott et al Oct. 13, 1942 FOREIGN APATENTS Country Date Germany Sept. 1, 1930

